PC Graham Davies said: "This plaque forms part of a memorial and is of great significance to the town. It is upsetting for people to see that the plaque has been taken.

"We would urge anyone who knows the identity of the thief, or the whereabouts of the plaque, to contact us immediately. We would also appeal to anyone who may have been offered the plaque for sale to get in touch."

It follows a raid earlier this week by the Metropolitan Police on a scrap metal yard in South East London, which recovered hundreds of memorial plaques from churches and crematoriums, a statue of Christ and entire intact cross among a major haul of items.

The Warrington bombings were made up of two separate attacks - the first in February when a bomb exploded at a district pressure gas storage facility.

No one was injured but a policeman was shot and wounded by one of the bombers when he stopped a van connected to the attacks.

The second bombing occurred on March 23 after The Samaritans received a coded message wrongly stating a bomb would be detonated outside a Boots shop in Liverpool.

Cheshire Police were warned about the threat but about 30 minutes later, at about 12:25pm two bombs exploded on Bridge Street in Warrington before the town centre could be evacuated.

One blast showered fifty children in a McDonalds with glass before the other detonated.

Johnathan died at the scene, while his babysitter survived. Tim received the full force of the blast and died when doctors switched his life support machine off. Fifty-four other people were injured, four of them seriously.

The parents of Tim Parry set up the Tim Parry Trust Fund to promote greater understanding between Britain and Ireland.

The plaque reads: 'The central water feature is in part a memorial to two local children who died following the terrorist bomb explosion in Bridge Stret in 1993. Young people helped the artist with the design work.'

The theft of the plaque follows an incident on April 21 when Spartakas Grachauskas, 25, was arrested and charged with attempting to steal the memorial. He is due at Manchester Crown Court on May 23.